Fixed #2925 -- Added missing exception import to admin.views.auth. Thanks, SmileyChris

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3925 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/admin/views/auth.py

 from django.contrib.admin.views.decorators import staff_member_required
 from django.contrib.auth.forms import UserCreationForm
 from django.contrib.auth.models import User
+from django.core.exceptions import PermissionDenied
 from django import forms, template
 from django.shortcuts import render_to_response
 from django.http import HttpResponseRedirect